Description of the Related Art
On die voltage regulation is a technique that is commonly used to lower power consumption and at the same time reduce system cost. On die regulators often use a monolithic structure placed next to the logic utilizing power being regulated. FIG. 1 illustrates a high level block diagram of such a structure. The system 100 includes a regulator 101 that regulates a voltage 103 and supplies a regulated voltage 105 to circuits 107 using the regulated voltage. The circuits 107 may be, e.g., a central processing unit (CPU) core. A regulator scheme is described in application Ser. No. 14/720,385, filed May 22, 2015, entitled “Droop Detection for Low-Dropout Regulator” naming Miguel Rodriguez et al. as inventors, Pub. No.: US 2016/0342166, which application is incorporated by reference herein. The regulation scheme includes a first slow control loop to control regulation for voltage changes due to such factors as temperature or power control settings. The regulation scheme includes a faster control loop to respond to sudden transient loading. The regulation scheme includes a droop detector to detect when the regulated voltage drops below a predetermined droop threshold due to sudden transient loading and responds quickly by injecting additional charge to maintain the regulated voltage within a tolerable margin.
However, the monolithic regulator has limited range due to the impedance of the power delivery network. In order to reduce the impedance, implementations using monolithic regulators typically utilize package planes to receive the regulated voltage from the regulator and distribute the regulated voltage. However, even low resistive package planes have a range of only approximately 4000-5000 microns in current process technologies before the regulator loses its effectiveness due to IR drop across the package plane.
FIG. 2A illustrates an existing regulation scheme. The always on (AON) package plane 201 receives power through bumps 202. The input to the regulator comes from the always on (AON) package plane 201 through package metal 203 and die metal 205 to the regulator logic 207. For ease of illustration, FIG. 2A ignores other connections that go through the package layers. The regulator logic 207 supplies the regulated voltage to the regulated package plane 209 through die metal 206 and package metal 204. The regulated package plane 209 then distributes the regulated voltage from the regulated package plane 209 to the bottom metal 215 on die through package metal vias 204 and die metal vias 206 for use by the circuits of the regulated voltage domain.
FIG. 2B shows another view of the existing regulation scheme where the input unregulated voltage goes from the always on package plane 201 to the metal layer M1 and then back up to a regulated package plane 209 for distribution to the regulated domain through the package metal vias 204 and die metal vias 206. If the regulated package plane 209 gets too large, the impedance eventually degrades the regulated voltage due to IR drop, and the regulation no longer functions effectively. That is, circuits close to the regulator logic 207 see a higher voltage than the circuits farthest away from the regulator. Thus, monolithic on die regulators cannot be scaled effectively. In addition, regulation adds cost because of the extra package layers, such as regulated package plane 209, needed to distribute the regulated voltage.
FIG. 3 illustrates another shortcoming of the monolithic regulators, which often form an electromagnetic (EM) bottleneck (current crowding) at their input 301 and output 303. Monolithic regulator schemes also create local routing congestion if the circuits being powered have many inputs/outputs.
Thus, improvements in voltage regulation is desirable particularly for large regulated structures.